Composite electrode

ABSTRACT

An apparatus is disclosed that includes an active storage layer including: a network of carbon nanotubes defining void spaces; and a carbonaceous material located in the void spaces and bound by the network of carbon nanotubes. In some cases, the active layer provides energy storage, e.g., in an ultracapacitor device.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/427,546 filed on May 31, 2019, which is acontinuation-in-part of PCT/US2017/064152 filed on Dec. 1, 2017, whichclaims the benefit of U.S. Provisional Application No. 62/429,727entitled “Composite Electrode” and filed Dec. 2, 2016, the entirecontents of which are incorporated herein by reference.

BACKGROUND

Carbon nanotubes (hereinafter referred to also as “CNTs”) are carbonstructures that exhibit a variety of properties. Many of the propertiessuggest opportunities for improvements in a variety of technology areas.These technology areas include electronic device materials, opticalmaterials as well as conducting and other materials. For example, CNTsare proving to be useful for energy storage in capacitors.

However, CNTs are typically expensive to produce and may present specialchallenges during electrode manufacturing. Accordingly, there is a needfor an electrode material that exhibits the advantageous properties ofCNTs while mitigating the amount of CNTs included in the material.

SUMMARY

The applicants have developed a composite electrode structure thatexhibits advantageous properties. In some embodiments, the electrodeexhibits the advantageous properties of CNTs while mitigating the amountof CNTs included in the material, e.g., to less than 10% by weight.

Electrodes of the type described herein may be used in ultracapacitorsto provide high performance (e.g., high operating, voltage, highoperating temperature, high energy density, high power density, lowequivalent series resistance, etc.).

In one aspect, an apparatus is disclosed including an active storagelayer including a network of carbon nanotubes defining void spaces; anda carbonaceous material located in the void spaces and bound by thenetwork of carbon nanotubes, wherein the active layer is configured toprovide energy storage.

In some embodiments, the active layer is substantially free from bindingagents. In some embodiments, the active layer consists of or consistsessentially of carbonaceous material. In some embodiments, the activelayer is bound together by electrostatic forces between the carbonnanotubes and the carbonaceous material. In some embodiments, thecarbonaceous material includes activated carbon.

In some embodiments, the carbonaceous material includes nanoform carbonother than carbon nanotubes.

In some embodiments, the network of carbon nanotubes makes up less than50% by weight of the active layer, less than 10% by weight of the activelayer, less than 5% by weight of the active layer, or less than 1% byweight of the active layer.

Some embodiments include an adhesion layer, e.g., a layer consisting ofor consisting essentially of carbon nanotubes. In some embodiments theadhesion layer is disposed between the active layer and an electricallyconductive layer.

In some embodiments, a surface of the conductive layer facing theadhesion layer includes a roughened or textured portion. In someembodiments, a surface of the conductive layer facing the adhesion layerincludes a nanostructured portion. In some embodiments, thenanostructured portion includes carbide “nanowhiskers”. Thesenanowhiskers are thin elongated structures (e.g., nanorods) that extendgenerally away from the surface of the conductor layer 102. Thenanowhiskers may have a radial thickness of less than 100 nm, 50 nm, 25,nm, 10 nm, or less, e.g., in the range of 1 nm to 100 nm or any subrangethereof. The nanowhisker may have a longitudinal length that is severalto many times its radial thickness, e.g., greater than 20 nm, 50 nm, 100nm, 200 nm, 300, nm, 400, nm, 500 nm, 1 μm, 5 μm, 10 μm, or more, e.g.,in the range of 20 nm to 100 μm or any subrange thereof.

In some embodiments, the active layer has been annealed to reduce thepresence of impurities.

In some embodiments, active layer has been compressed to deform at leasta portion of the network of carbon nanotubes and carbonaceous material.

Some embodiments include an electrode including the active layer. Someembodiments include an ultracapacitor including the electrode, In someembodiments, the ultracapacitor has an operating voltage greater than1.0 V, 2.0 V, 2.5 V 3.0 V, 3.1 V, 3.2 V, 3.5 V, 4.0 V or more.

In some embodiments, the ultracapacitor has a maximum operatingtemperature of at least 250 C at an operating voltage of at least 1.0 Vfor a lifetime of at least 1,000 hours. In some embodiments, theultracapacitor has a maximum operating temperature of at least 250 C atan operating voltage of at least 2.0 V for a lifetime of at least 1,000hours. In some embodiments, the ultracapacitor has a maximum operatingtemperature of at least 250 C at an operating voltage of at least 3.0 Vfor a lifetime of at least 1,000 hours. In some embodiments, theultracapacitor has a maximum operating temperature of at least 250 C atan operating voltage of at least 4.0 V for a lifetime of at least 1,000hours. In some embodiments, the ultracapacitor has a maximum operatingtemperature of at least 300 C at an operating voltage of at least 1.0 Vfor a lifetime of at least 1,000 hours. In some embodiments, theultracapacitor has a maximum operating temperature of at least 300 C atan operating voltage of at least 2.0 V for a lifetime of at least 1,000hours. In some embodiments, the ultracapacitor has a maximum operatingtemperature of at least 300 C at an operating voltage of at least 3.0 Vfor a lifetime of at least 1,000 hours. In some embodiments, theultracapacitor has a maximum operating temperature of at least 300 C atan operating voltage of at least 4.0 V for a lifetime of at least 1,000hours.

In another aspect, a method including: dispersing carbon nanotubes in asolvent to form a dispersion; mixing the dispersion with carbonaceousmaterial to form a slurry; applying the slurring in a layer; and dryingthe slurry to substantially remove the solvent to form an active layerincluding a network of carbon nanotubes defining void spaces and acarbonaceous material located in the void spaces and bound by thenetwork of carbon nanotubes. Some embodiment include forming or applyinga layer of carbon nanotubes to provide an adhesion layer on a conductivelayer.

In some embodiments, the applying step including applying the slurryonto the adhesion layer.

Various embodiments may include any of the forgoing elements orfeatures, or any elements or features described herein either alone orin any suitable combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an electrode.

FIG. 2 is an illustration of a detailed view of an active layer of anelectrode.

FIG. 3 is a schematic of a two-sided electrode.

FIG. 4 is a flow chart illustrating a method of making an active layerfor an electrode.

FIG. 5 is a flow chart illustrating a method of making an adhesion layerfor an electrode.

FIG. 6 is a schematic diagram of an exemplary mixing apparatus.

FIG. 7A is a schematic diagram of coating apparatus featuring a slotdie.

FIG. 7B is a schematic diagram of coating apparatus featuring a doctorblade.

FIG. 8A is a schematic of an ultracapacitor.

FIG. 8B is a schematic of an ultracapacitor without a separator.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary embodiment of an electrode 100 isdisclosed for use in an energy storage device, such as an ultracapacitoror battery. The electrode includes an electrically conductive layer 102(also referred to herein as a current collector), an adhesion layer 104,and an active layer 106. When used in an ultracapacitor of the typedescribed herein, the active layer 106 may act as energy storage media,for example, by providing a surface interface with an electrolyte (notshown) for formation of an electric double layer (sometimes referred toin the art as a Helmholtz layer). In some embodiments, the adhesionlayer 104 may be omitted, e.g., in cases where the active layer 106exhibits good adhesion to the electrically conductive layer 102.

In some embodiments, the active layer 106 may be thicker than theadhesion layer 104, e.g, 1.5, 2.0, 5.0, 10, 20, 30, 40, 50, 60, 70, 80,90, 100, 500, 1,000 or more times the thickness of the adhesion layer104. For example, in some embodiments, the thickness of the active layer106 may be in the range of 1.5 to 1,000 times the thickness of theadhesion layer 104 (or any subrange thereof, such as 5 to 100 times).For example, in some embodiments the active layer 106 may have athickness in the in the range of 0.5 to 2500 μm or any subrange thereof,e.g., 5 μm to 150 μm. In some embodiments the adhesion layer 104 mayhave a thickness in the range of 0.5 μm to 50 μm or any subrangethereof, e.g., 1 μm to 5 μm.

Referring to FIG. 2, in some embodiments, the active layer 106 iscomprised of carbonaceous material 108 (e.g., activated carbon) boundtogether by a matrix 110 of CNTs 112 (e.g., a webbing or network formedof CNTs). In some embodiments, e.g., where the length of the CNTs islonger than the thickness of the active layer 106, the CNTs 112 formingthe matrix 110 may lie primarily parallel to a major surface of theactive layer 106. Not that although as shown the CNTs 112 form straightsegments, in some embodiments, e.g., where longer CNTs are used, thesome or all of the CNTs may instead have a curved or serpentine shape.For example, in cases where the carbonaceous material 108 includes lumpsof activated carbon, the CNTs 112 may curve and wind between the lumps.

In some embodiments, the active layer is substantially free of any otherbinder material, such as polymer materials, adhesives, or the like. Inother words, in such embodiments, the active layer is substantially freefrom any material other than carbon. For example, in some embodiments,the active layer may be at least about 90 wt %, 95 wt %, 96 wt %, 97 wt%, 98 wt %, 99 wt %, 99.5 wt %, 99.9 wt %, 99.99 wt %, 99.999 wt %, ormore elemental carbon by mass. Despite this, the matrix 110 operated tobind together the carbonaceous material 108, e.g., to maintain thestructural integrity of the active layer 106 without flaking,delamination, disintegration, or the like.

It has been found that use of an active layer substantially free of anynon-carbon impurities substantially increases the performance of theactive layer in the presence of high voltage differentials, hightemperatures, or both. Not wishing to be bound by theory, it is believedthat the lack of impurities prevents the occurrence of unwanted chemicalside reactions which otherwise would be promoted in high temperature orhigh voltage conditions.

As noted above, in some embodiments, the matrix 110 of carbon nanotubesprovides a structural framework for the active layer 106, with thecarbonaceous material 108 filling the spaces between the CNTs 112 of thematrix 110. In some embodiments, electrostatic forces (e.g., Van DerWaals forces) between the CNTs 112 within the matrix 110 and between thematrix 112 and the other carbonaceous material 108 may providesubstantially all of the binding forces maintaining the structuralintegrity of the layer.

In some embodiments, the CNTs 112 may include single wall nanotubes(SWNT), double wall nanotubes (DWNT), or multiwall nanotubes (MWNT), ormixtures thereof. Although a matrix 110 of individual CNTs 112 is shown,in some embodiments, the matrix may include interconnected bundles,clusters or aggregates of CNTs. For example, in some embodiments wherethe CNTs are initially formed as vertically aligned, the matrix may bemade up at least in part of brush like bundles of aligned CNTs.

In order to provide some context for the teachings herein, reference isfirst made to U.S. Pat. No. 7,897,209, entitled “Apparatus and Methodfor Producing Aligned Carbon Nanotube Aggregate.” The foregoing patent(the “'209 patent”) teaches a process for producing aligned carbonnanotube aggregate. Accordingly, the teachings of the '209 patent, whichare but one example of techniques for producing CNTs in the form of analigned carbon nanotube aggregate, may be used to harvest CNTs referredto herein. Advantageously, the teachings of the '209 patent may be usedto obtain long CNTs having high purity. In other embodiments, any othersuitable method known in the art for producing CNTs may be used.

In some embodiments the active layer 106 may be formed as follows. Afirst solution (also referred to herein as a slurry) is provided thatincludes a solvent and a dispersion of carbon nanotubes, e.g.,vertically aligned carbon nanotubes. A second solution (also referred toherein as a slurry) may be provided that includes a solvent with carbondisposed therein. This carbon addition includes at least one form ofmaterial that is substantially composed of carbon. Exemplary forms ofthe carbon addition include, for example, at least one of activatedcarbon, carbon powder, carbon fibers, rayon, graphene, aerogel,nanohorns, carbon nanotubes and the like. While in some embodiments, thecarbon addition is formed substantially of carbon, it is recognized thatin alternative embodiments the carbon addition may include at least someimpurities, e.g., additives included by design.

In some embodiments, forming the first and/or second solution includeintroducing mechanical energy into the mixture of solvent and carbonmaterial, e.g., using a sonicator (sometimes referred to as a sonifier)or other suitable mixing device (e.g., a high shear mixer). In someembodiments, the mechanical energy introduced into the mixture perkilogram of mixture is at least 0.4 kWh/kg, 0.5 kWh/kg, 0.6 kWh/kg, 0.7kWh/kg, 0.8 kWh/kg, 0.9 kWh/kg, 1.0 kWh/kg, or more. For example, themechanical energy introduced into the mixture per kilogram of mixturemay be in the range of 0.4 kWh/kg to 1.0 kWh/kg or any subrange thereofsuch as 0.4 kWh/kg to 0.6 kWh/kg.

In some embodiments, the solvents used may include an anhydrous solvent.For example, the solvent may include at least one of ethanol, methanol,isopropyl alcohol, dimethyl sulfoxide, dimethylformamide, acetone,acetonitrile, and the like.

As noted above, the two solutions may be subjected to “sonication”(physical effects realized in an ultrasonic field). With regard to thefirst solution, the sonication is generally conducted for a period thatis adequate to tease out, fluff or otherwise parse the carbon nanotubes.With regard to the second solution, the sonication is generallyconducted for a period that is adequate to ensure good dispersion ormixing of the carbon additions within the solvent. In some embodiments,other techniques for imparting mechanical energy to the mixtures may beused in addition or alternative to sonication, e.g, physical mixingusing stirring or impeller.

Once one or both of the first solution and the second solution have beenadequately sonicated, they are then mixed together, to provide acombined solution and may again be sonicated. Generally, the combinedmixture is sonicated for a period that is adequate to ensure good mixingof the carbon nanotubes with the carbon addition. This second mixing(followed by suitable application and drying steps as described below)results in the formation of the active layer 106 containing the matrix110 of CNTs 112, with the carbon addition providing the othercarbonaceous material 108 filling the void spaces of the matrix 110.

In some embodiments, mechanical energy may be introduced to the combinedmixture using a sonicator (sometimes referred to as a sonifier) or othersuitable mixing device (e.g., a high shear mixer). In some embodiments,the mechanical energy into the mixture per kilogram of mixture is atleast 0.4 kWh/kg, 0.5 kWh/kg, 0.6 kWh/kg, 0.7 kWh/kg, 0.8 kWh/kg, 0.9kWh/kg, 1.0 kWh/kg, or more. For example, the mechanical energyintroduced into the mixture per kilogram of mixture may be in the rangeof 0.4 kWh/kg to 1.0 kWh/kg or any subrange thereof such as 0.4 kWh/kgto 0.6 kWh/kg.

In some embodiments, the combined slurry may be cast wet directly ontothe adhesion layer 104 or the conductive layer 102, and dried (e.g., byapplying heat or vacuum or both) until substantially all of the solventand any other liquids have been removed, thereby forming the activelayer 106. In some such embodiments it may be desirable to protectvarious parts of the underlying layers (e.g., an underside of aconductive layer 102 where the current collector is intended for twosided operation) from the solvent, e.g., by masking certain areas, orproviding a drain to direct the solvent.

In other embodiments, the combined slurry may be dried elsewhere andthen transferred onto the adhesion layer 104 or the conductive layer 102to form the active layer 106, using any suitable technique (e.g.,roll-to-roll layer application). In some embodiments the wet combinedslurry may be placed onto an appropriate surface and dried to form theactive layer 106. While any material deemed appropriate may be used forthe surface, exemplary material includes PTFE as subsequent removal fromthe surface is facilitated by the properties thereof. In someembodiments, the active layer 106 is formed in a press to provide alayer that exhibits a desired thickness, area and density.

In some embodiments, the average length of the CNTs 112 forming thematrix 110 may be at least 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 50 pin,100 μm, 200 μm, 300, μm, 400 μm, 500 μm, 600 μm, 7000 μm, 800 μm, 900μm, 1,000 μm or more. For example, in some embodiments, the averagelength of the CNTs 112 forming the matrix 110 may be in the range of 1μm to 1,000 μm, or any subrange thereof, such as 1 μm to 600 in. In someembodiments, more than 50%, 60%, 70%, 80%, 90%, 95%, 99% or more of theCNTs 112 may have a length within 10% of the average length of the CNTs112 making up the matrix 110.

In various embodiments, the other carbonaceous material 108 can includecarbon in a variety forms, including activated carbon, carbon black,graphite, and others. The carbonaceous material can include carbonparticles, including nanoparticles, such as nanotubes, nanorods,graphene in sheet, flake, or curved flake form, and/or formed intocones, rods, spheres (buckyballs) and the like.

Applicants have found unexpected result that an active layer of the typeherein can provide exemplary performance (e.g., high conductivity, lowresistance, high voltage performance, and high energy and power density)even when the mass fraction of CNTs in the layer is quite low. Forexample, in some embodiments, the active layer may be at least about 50wt %, 60 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %, 95 wt %, 96wt % 97 wt %, 98 wt %, 99 wt %, 99.5 wt %, or more elemental carbon in aform other than CNT (e.g., activated carbon). In particular, for certainapplications involving high performance ultracapacitors, active layers106 that are in the range of 95 wt % to 99 wt % activated carbon (withthe balance CNTs 112), have been shown to exhibit excellent performance.

In some embodiments, the matrix 110 of CNTs 112 form an interconnectednetwork of highly electrically conductive paths for current flow (e.g.ion transport) through the active layer 106. For example, in someembodiments, highly conductive junctions may occur at points where CNTs112 of the matrix 110 intersect with each other, or where they are inclose enough proximity to allow for quantum tunneling of charge carriers(e.g., ions) from one CNT to the next. While the CNTs 112 may make up arelatively low mass fraction of the active layer (e.g., less than 10 wt%, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt % or less, e.g., in the range of0.5 wt % to 10 wt % or any subrange thereof such as 1 wt % to 5.0 wt %),the interconnected network of highly electrically conductive pathsformed in the matrix 110 may provide long conductive paths to facilitatecurrent flow within and through the active layer 106 (e.g. conductivepaths on the order of the thickness of the active layer 106).

For example, in some embodiments, the matrix 110 may include one or morestructures of interconnected CNTs, where the structure has an overalllength in along one or more dimensions longer than 2, 3, 4, 5, 10, 20,50, 100, 500, 1,000, 10,000 or more times the average length of thecomponent CNTs making up the structure. For example, in someembodiments, the matrix 110 may include one or more structures ofinterconnected CNTs, where the structure has an overall in the range of2 to 10,000 (or any subrange thereof) times the average length of thecomponent CNTs making up the structure For example, in some embodimentsthe matrix 110 may include highly conductive pathways having a lengthgreater than 100 μm, 500 μm, 1,000 μm, 10,000 μm or more, e.g., in therange of 100 μm-10,000 μm of any subrange thereof.

As used herein, the term “highly conductive pathway” is to be understoodas a pathway formed by interconnected CNTs having an electricalconductivity higher than the electrical conductivity of the othercarbonaceous material 108 (e.g., activated carbon), surrounding thatmatrix 110 of CNTs 112.

Not wishing to be bound by theory, in some embodiments the matrix 110can characterized as an electrically interconnected network of CNTexhibiting connectivity above a percolation threshold. Percolationthreshold is a mathematical concept related to percolation theory, whichis the formation of long-range connectivity in random systems. Below thethreshold a so called “giant” connected component of the order of systemsize does not exist; while above it, there exists a giant component ofthe order of system size.

In some embodiments, the percolation threshold can be determined byincreasing the mass fraction of CNTs 112 in the active layer 106 whilemeasuring the conductivity of the layer, holding all other properties ofthe layer constant. In some such cases, the threshold can be identifiedwith the mass fraction at which the conductivity of the layer sharplyincreases and/or the mass fraction above which the conductivity of thelayer increases only slowly with increases with the addition of moreCNTs. Such behavior is indictive of crossing the threshold required forthe formation of interconnected CNT structures that provide conductivepathways with a length on the order of the size of the active layer 106.

Returning to FIG. 1, in some embodiments, one or both of the activelayer 106 and the adhesion layer 104 may be treated by applying heat toremove impurities (e.g., functional groups of the CNTs, and impuritiessuch as moisture, oxides, halides, or the like). For example, in someembodiments, one or both of the layers can be heated to at least 100 C,150 C, 200 C, 250 C, 300 C, 350 C, 400 C, 450 C, 500 C or more for atleast 1 minute, 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 3hours, 12 hours, 24 hours, or more. For example, in some embodiments thelayers may be treated to reduce moisture in the layer to less that 1,000ppm, 500 ppm, 100 ppm, 10 ppm, 1 ppm, 0.1 ppm or less.

Returning to FIG. 1, in some embodiments, the adhesion layer 104 may beformed of carbon nanotubes. For example, in some embodiments, theadhesion layer 104 may be at least about 50%, 75%, 80%, 90%, 95%, 96%97%, 98%, 99%, 99.5%, 99.9%, 99.99%, 99.999% by mass CNTs. In someembodiments, the CNTs may be grown directly on the conductive layer 102,e.g., using the chemical vapor deposition techniques such as thosedescribed in U.S. Patent Pub. No 2013/0045157 entitled “In-lineManufacture of Carbon Nanotubes” and published Feb. 21, 2013. In someembodiments, the CNTs may be transferred onto the conductive layer 102,e.g., using wet or dry transfer processes, e.g., of the type describede.g., in U.S. Patent Pub. No. 2013/0044405 entitled “High Power and HighEnergy Electrodes Using Carbon Nanotubes” and published Feb. 21, 2013.In some embodiments, the adhesion layer 104 adheres to the overlyingactive layer 106 using substantially only electrostatic forces (e.g.,Van Der Waals attractions) between the CNTs of the adhesion layer 104and the carbon material and CNTs of the active layer 106.

In some embodiments, the CNTs of the adhesion layer 104 may includesingle wall nanotubes (SWNT), double wall nanotubes (DWNT), or multiwallnanotubes (MWNT), or mixtures thereof. In some embodiments the CNTs maybe vertically aligned. In one particular embodiment, the CNTs of theadhesion layer 104 may be primarily or entirely SWNTs and/or DWNTs,while the CNTs of the active layer 106 a primarily or entirely MWNTs.For example, in some embodiments, the CNTs of the of the adhesion layer104 may be at least 75%, at least 90%, at least 95%, at least 99% ormore SWNT or at least 75%, at least 90%, at least 95%, at least 99% ormore DWNT. In some embodiments, the CNTs of the of the active layer 106may be at least 75%, at least 90%, at least 95%, at least 99% or moreMWNT.

In some embodiments, the adhesion layer 104 may be formed by applyingpressure to a layer of carbonaceous material. In some embodiments, thiscompression process alters the structure of the adhesion layer 104 in away that promotes adhesion to the active layer 106. For example, in someembodiments pressure may be applied to layer comprising a verticallyaligned array of CNT or aggregates of vertically aligned CNT, therebydeforming or breaking the CNTs.

In some embodiments, the adhesion layer may be formed by casting a wetslurry of CNTs (with or without additional carbons) mixed with a solventonto the conductive layer 102. In various embodiments, similartechniques to those described above for the formation of the activelayer 106 from a wet slurry may be used.

In some embodiments, mechanical energy may be introduced to the wetslurry using a sonicator (sometimes referred to as a sonifier) or othersuitable mixing device (e.g., a high shear mixer). In some embodiments,the mechanical energy into the mixture per kilogram of mixture is atleast 0.4 kWh/kg, 0.5 kWh/kg, 0.6 kWh/kg, 0.7 kWh/kg, 0.8 kWh/kg, 0.9kWh/kg, 1.0 kWh/kg, or more. For example, the mechanical energyintroduced into the mixture per kilogram of mixture may be in the rangeof 0.4 kWh/kg to 1.0 kWh/kg or any subrange thereof such as 0.4 kWh/kgto 0.6 kWh/kg.

In some embodiments, the solid carbon fraction of the wet slurry may beless than 10 wt %, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt, 0.5 wt 5, 0.1wt % or less, e.g., in the range of 0.1 wt to 10 wt % or any subrangethereof such as 0.1 wt to 2 wt %.

In various embodiments, the conductive layer 102 may be made of asuitable electrically conductive material such as a metal foil (e.g., analuminum foil). In some embodiments, the surface of the conductive layer102 may be roughened, patterned, or otherwise texturized, e.g., topromote adhesion to the adhesion layer 104 and good electricalconductance from the active layer 106. For example, in some embodiments,the conductive layer may be etched (e.g., mechanically or chemically).In some embodiments, the conductive layer 102 may have a thickness inthe range of 1 μm to 1,000 μm or any subrange thereof such as 5 μm to 50μm.

In some embodiments, the conductive layer 102 may include ananostructured surface. For example, as described in International Pub.No. WO 2016/057983 entitled “Nanostructured Electrode for Energy StorageDevice” published Apr. 14, 2016, the conductive layer may have a topsurface that includes nanoscale features such as whiskers (e.g., carbidewhiskers) that promote adhesion to the adhesion layer 104 and goodelectrical conductance from the active layer 106. An exemplary currentcollector is the current collector available from Toyo Aluminum K.K.under the trade name TOYAL-CARBO®.

In some embodiments, one or both of the active layer 106 and theadhesion layer 104 may be treated by applying heat and/or vacuum toremove impurities (e.g., functional groups of the CNTs, and impuritiessuch as moisture, oxides, halides, or the like).

In some embodiments, one or both of the active the active layer 106 andthe adhesion layer 104 may be compressed, e.g., to break some of theconstituent CNTs or other carbonaceous material to increase the surfacearea of the respective layer. In some embodiments, this compressiontreatment may increase one or more of adhesion between the layers, iontransport rate within the layers, and the surface area of the layers. Invarious embodiments, compression can be applied before or after therespective layer is applied to or formed on the electrode 100.

In some embodiments, the adhesion layer 104 may be omitted, such thatthe active layer 106 is disposed directly on the conductive layer 102.

Referring to FIG. 3, in some embodiments, the electrode 100 may bedouble sided, with an adhesion layer 104 and active layer 106 formed oneach of two opposing major surfaces of the conductive layer 102. In someembodiments, the adhesion layer 104 may be omitted on one or both sidesof the two-sided electrode 100.

Referring to FIG. 4, an exemplary embodiment of method 200 of making theactive layer 106 of electrode 100 is described. In step 201, CNTs aredispersed in a solvent to form a dispersion of CNTs. In someembodiments, the dispersion may be formed using any of the techniquesdescribed in U.S. Patent Pub. No. 2013/0044405 entitled “High Power andHigh Energy Electrodes Using Carbon Nanotubes” published Feb. 21, 2013including stirring, sonication, or a combination of the two. In variousembodiments, any suitable solvent may be used, including, for example.ethanol, methanol, isopropyl alcohol, dimethyl sulfoxide,dimethylformamide, acetone, acetonitrile, and the like. In general, itis advantageous to choose a solvent that will be substantiallyeliminated in the drying step 204 described below, e.g., using heatand/or vacuum drying techniques.

In some embodiments, the mixture of CNTs and solvents may be passedthrough a filter, e.g., an array of micro channels (e.g., havingchannels with diameters on the order of the radial size of the CNTs) tohelp physically separate the CNTs and promote dispersion.

In some embodiments, the CNT dispersion may be formed without theaddition of surfactants, e.g., to avoid the presence of impuritiesderived from these surfactants at the completion of the method 200.

In step 202, the CNT dispersion is mixed with carbonaceous material(e.g., activated carbon) to form a slurry. In some embodiments, theslurry may be formed using any of the techniques described in U.S.Patent Pub. No. 2013/0044405, including stirring, sonication, or acombination of the two. In some embodiments, the slurry may have solidcarbon fraction of less than 20 wt %, 15 wt %, 10 wt %, 5 wt %, 2 wt %,1 wt %, or less, e.g., in the range of 1 wt % to 20 wt % or any subrangethereof such as 4% to 6%. The mass ratio of CNTs to other carbonaceousmaterial in the slurry may be less than 1:5, 1:10, 1:15, 1:20, 1:50,1:100, or less, e.g., in the range of 1:10 to 1:20 or any subrangethereof.

In step 203, the slurry is applied to either the adhesion layer 104 or,if the adhesion layer 104 is omitted, the conductive layer 102 of theelectrode 100. In some embodiments, the slurry may be formed into asheet, and coated onto the electrode. For example, in some embodiments,slurry may be applied to through a slot die to control the thickness ofthe applied layer. In other embodiments, the slurry may be applied tothe conductive layer 102, and then leveled to a desired thickness, e.g.,using a doctor blade.

In some embodiments, the slurry may be compressed (e.g., using acalendaring apparatus) before or after being applied to the electrode100. In some embodiments, the slurry may be partially or completelydried (e.g., by applying heat, vacuum or a combination thereof) duringthis step 203.

In step 204, if the slurry has not dried, or has been only partiallydried during step 203, the slurry applied to the electrode is fullydried, (e.g., by applying heat, vacuum or a combination thereof). Insome embodiments, substantially all of the solvent (and any othernon-carbonaceous material such as dispersing agents) is removed from theactive layer 106. In some embodiments, if impurities remain followingthe drying step, and additional step of heating (e.g. baking orannealing) the layer may be performed. For example, in some embodiments,one or both of the active the active layer 106 and the adhesion layer104 may be treated by applying heat to remove impurities (e.g.,functional groups of the CNTs, and impurities such as moisture, oxides,halides, or the like).

Referring to FIG. 5, an exemplary embodiment of method 300 of making theadhesion layer 104 of electrode 100 is described. In step 301, CNTs aredispersed in a solvent to form a dispersion of CNTs. In someembodiments, the dispersion may be formed using any of the techniquesdescribed in U.S. Patent Pub. No. 2013/0044405 including stirring,sonication, or a combination of the two. In various embodiments, anysuitable solvent may be used, including, for example an organic solventsuch as isopropyl alcohol, acetonitrile or propylene carbonate. Ingeneral, it is advantageous to choose a solvent that will besubstantially eliminated in the drying step 304 described below.

In some embodiments, the mixture of CNTs and solvents may be passedthrough a filter, e.g., an array of micro channels (e.g., havingchannels with diameters on the order of the radial size of the CNTs) tohelp physically separate the CNTs and promote dispersion.

In some embodiments, the CNT dispersion may be formed without theaddition of surfactants, e.g., to avoid the presence of impuritiesderived from these surfactants at the completion of the method 300.

In step 302, the CNT dispersion may optionally be mixed with additionalcarbonaceous material (e.g., activated carbon) to form a slurry. In someembodiments, the additional carbonaceous material may be omitted, suchthat the slurry is made up of CNTs dispersed in a solvent. In someembodiments, the slurry may have solid fraction of less than 5 wt %, 4wt %, 3 wt %, 2 wt %, 1 wt %, 0.5 wt %, 0.1 wt %, or less, e.g., in therange of 0.1 to 5 wt % or any subrange thereof.

In step 303, the slurry is applied to the conductive layer 102 of theelectrode 100. In some embodiments, the slurry may be coated onto theelectrode. For example, in some embodiments, slurry may be applied tothrough a slot die to control the thickness of the applied layer. Inother embodiments, the slurry may be applied to the conductive layer102, and then leveled to a desired thickness, e.g., using a doctorblade.

In some embodiments, the slurry may be compressed (e.g., using acalendaring apparatus) before or after being applied to the electrode100. In some embodiments, the slurry may be partially or completelydried (e.g., by applying heat, vacuum or a combination thereof) duringthis step 303.

In step 304, if the slurry has not dried, or has been only partiallydried during step 203, the slurry applied to the electrode is fullydried, (e.g., by applying heat, vacuum or a combination thereof). Insome embodiments, substantially all of the solvent (and any othernon-carbonaceous material such as dispersing agents) is removed from theactive layer 106. In some embodiments, if impurities remain followingthe drying step, and additional step of heating (e.g. baking orannealing) the layer may be performed. For example, in some embodiments,one or both of the active the active layer 106 and the adhesion layer104 may be treated by applying heat to remove impurities (e.g.,functional groups of the CNTs, and impurities such as moisture, oxides,halides, or the like).

In some embodiments, the method 300 for forming an adhesion layer 104and method 200 for forming an active layer 106 may be performed inseries to successively form the adhesion layer 104 followed by theoverlaying active layer 106. In some embodiments, the foregoing methodsmay be repeated, e.g., to form a two-sided electrode of the typedescribed herein.

Advantageously, in some embodiments, the method 300 for forming anadhesion layer 104 and/or method 200 for forming an active layer 106 maybe implemented as a roll-to-roll processes, e.g., to allow volumeproduction of electrode sheets several tens of meters long or more.

FIG. 6 shows an exemplary mixing apparatus 400 for implementing themethod 300 for forming an adhesion layer 104 and/or method 200 forforming an active layer 106. In the interest of brevity, the apparatus400 will be described for use in forming active layer 106 using method200. However, as will be apparent to one skilled in the art, theapparatus 400 can easily be configured to implement the method 300 forforming an adhesion layer 104.

The apparatus 400 includes a mixing vessel 401. The mixing vesselreceives a slurry composed of a solvent, carbon nanotubes, and(optionally) additional carbonaceous material of the type describedabove. In some embodiments, this slurry (or components thereof) may beinitially formed in the mixing vessel 401. In other embodiments, theslurry may be formed elsewhere and then transferred to the mixing vessel401.

In some embodiments the mixing vessel 401 may include one or moremechanisms for mixing the slurry, such as an impeller or high sheermixer. In some embodiments, a mixing mechanism may be provided which iscapable of stirring the slurry at a controlled rate, e.g., of up to 1000rotations per minute (RPM) or more. In some embodiments, the mixingvessel may include one or more devices for applying mechanical energy tothe slurry, such as a sonicator, mixer (e.g., a high shear mixer),homogenizer, or any other suitable device known in the art. In someembodiments, the mixing vessel may be temperature controlled, e.g.,using one or more heating and/or cooling elements such as electricheaters, tubing for circulating chilled water, or any other such devicesknown in the art.

Slurry from the mixing vessel 401 may be circulated through a flow line402, e.g. a pipe or tubing, using a pump 403. Pump 403 may be anysuitable configuration, such as a peristaltic pump. A flow meter 404 maybe provided to measure the rate of slurry flow through the flow line402. A filter 405 may be provided to filter the slurry flowing throughthe flow line 402, e.g., to remove clumps of solid material having asize above a desired threshold.

In some embodiments, e.g., where mixing vessel 401 does not include asonicator, an in-line sonicator 406 may be provided to sonicate slurryflowing through the flow line 402. For example, in some embodiments aflow through sonicator such as the Branson Digital SFX-450 sonicatoravailable commercially from Thomas Scientific of 1654 High Hill RoadSwedesboro, N.J. 08085 U.S.A may be used.

In some embodiments, a temperature control device 407, such as a heatexchanger arranged in a sleeve disposed about the flow line 402, isprovided to control the temperature of the slurry flowing through theflow line 402.

In some embodiments a valve 408 is provided which can be selectivelycontrolled to direct a first portion of the slurry flowing through flowline 402 to be recirculated back to the mixing vessel 401, while asecond portion is output externally, e.g., to a coating apparatus 500.In some embodiments, a sensor 409 such as a pressure sensor or flow ratesensor is provided to sense one or more aspects of the output portion ofslurry.

In various embodiments any or all of the elements of apparatus 400 maybe operatively connected to one or more computing devices to provide forautomatic monitoring and/or control of the mixing apparatus 400. Forexample, the sonicator 406 may include digital controls for controllingits operating parameters such as power and duty cycle.

In various embodiments, the coating apparatus 500 may be any suitabletype known in the art. For example, FIG. 7A shows an exemplaryembodiment of coating apparatus 500 featuring a slot die 501 thatdistributes slurry received from a source such as the mixing apparatus400 through a distribution channel 502 onto a substrate 503 (e.g., theconductive layer 102, either bare or already coated with adhesion layer104) which moves across a roller 504. Setting the height of the slot dieabove the substrate 503 on the roller 504 and controlling the flow rateand/or pressure of the slurry in the channel 502 allows for control ofthe thickness and density of the applied coating. In some embodiments,channel 502 may include one or more reservoirs to help ensure consistentflow of slurry to provide uniform coating during operation.

FIG. 7B shows an exemplary embodiment of coating apparatus 500 featuringa doctor blade 601 that levels slurry received from a source such as themixing apparatus 400 that is applied through on or more applicators 602(one is shown) onto a substrate 603 (e.g., the conductive layer 102,either bare or already coated with adhesion layer 104) which movesacross a roller 604. The direction of travel of the substrate 603 isindicated by the heavy dark arrow. Setting the height of the doctorblade 601 above the substrate 603 on the roller 604 and controlling theflow rate and/or pressure of the slurry through the applicator 602allows for control of the thickness and density of the applied coating.Although a single doctor blade 601 is shown, multiple blades may beused, e.g., a first blade to set a rough thickness of the coating, and asecond blade positioned down line form the first blade to provide finesmoothing of the coating.

Further, disclosed herein are capacitors incorporating the electrodethat provide users with improved performance in a wide range oftemperatures. Such ultracapacitors may comprise an energy storage celland an electrolyte system within an hermetically sealed housing, thecell electrically coupled to a positive contact and a negative contact,wherein the ultracapacitor is configured to operate at a temperatureswithin a temperature range between about −100 degrees Celsius to about300 degrees Celsius or more, or any subrange thereof, e.g., −40 C to 200C, −40 C to 250 C, −40 C to 300 C, 0 C to 200 C, 0 C to 250 C, 0 C to300 C. In some embodiments such ultracapacitors can operate a voltagesof 1.0 V, 2.0 V, 3.0 V, 3.2 V, 3.5 V. 4.0 V, or more, e.g., forlifetimes exceeding 1,000 hours.

As shown in FIGS. 8A and 8B, exemplary embodiments of a capacitor areshown. In each case, the capacitor is an “ultracapacitor 10.” Thedifference between FIG. 8A and FIG. 8B is the inclusion of a separatorin exemplary ultracapacitor 10 of FIG. 8A. The concepts disclosed hereingenerally apply equally to any exemplary ultracapacitor 10. Certainelectrolytes of certain embodiments are uniquely suited to constructingan exemplary ultracapacitor 10 without a separator. Unless otherwisenoted, the discussion herein applies equally to any ultracapacitor 10,with or without a separator.

The exemplary ultracapacitor 10 is an electric double-layer capacitor(EDLC). The EDLC includes at least one pair of electrodes 3 (where theelectrodes 3 may be referred to as a negative electrode 3 and a positiveelectrode 3, merely for purposes of referencing herein). When assembledinto the ultracapacitor 10, each of the electrodes 3 (which may each bean electrode 100 of the type shown in FIG. 1 above) presents a doublelayer of charge at an electrolyte interface. In some embodiments, aplurality of electrodes 3 is included (for example, in some embodiments,at least two pairs of electrodes 3 are included). However, for purposesof discussion, only one pair of electrodes 3 are shown. As a matter ofconvention herein, at least one of the electrodes 3 uses a carbon-basedenergy storage media 1 (e.g., the active layer 106 of electrode 100shown in FIG. 1), and it assumed that each of the electrodes includesthe carbon-based energy storage media 1. It should be noted that anelectrolytic capacitor differs from an ultracapacitor because metallicelectrodes differ greatly (at least an order of magnitude) in surfacearea.

Each of the electrodes 3 includes a respective current collector 2 (alsoreferred to as a “charge collector”), which may be the conductive layer102 of electrode 100 shown in FIG. 1. In some embodiments, theelectrodes 3 are separated by a separator 5. In general, the separator 5is a thin structural material (usually a sheet) used to separate thenegative electrode 3 from the positive electrode 3. The separator 5 mayalso serve to separate pairs of the electrodes 3. Once assembled, theelectrodes 3 and the separator 5 provide a storage cell 12. Note that,in some embodiments, the carbon-based energy storage media 1 may not beincluded on one or both of the electrodes 3. That is, in someembodiments, a respective electrode 3 might consist of only the currentcollector 2. The material used to provide the current collector 2 couldbe roughened, anodized or the like to increase a surface area thereof.In these embodiments, the current collector 2 alone may serve as theelectrode 3. With this in mind, however, as used herein, the term“electrode 3” generally refers to a combination of the energy storagemedia 1 and the current collector 2 (but this is not limiting, for atleast the foregoing reason).

At least one form of electrolyte 6 is included in the ultracapacitor 10.The electrolyte 6 fills void spaces in and between the electrodes 3 andthe separator 5. In general, the electrolyte 6 is a substance thatdisassociates into electrically charged ions. A solvent that dissolvesthe substance may be included in some embodiments of the electrolyte 6,as appropriate. The electrolyte 6 conducts electricity by ionictransport.

In some embodiments, the electrolyte 6 may be in gelled or solid form(e.g., an ionic liquid impregnated polymer layer). Examples of suchelectrolytes are provided in International Publication No. WO2015/102716 entitled “ADVANCED ELECTROLYTES FOR HIGH TEMPERATURE ENERGYSTORAGE DEVICE” and published Jul. 9, 2015.

In other embodiments, the electrolyte 6 may be in non-aqueous liquidform, e.g., an ionic liquid, e.g., of a type suitable for hightemperature applications. Examples of such electrolytes are provided inInternational Publication No. WO 2015/102716 entitled “ADVANCEDELECTROLYTES FOR HIGH TEMPERATURE ENERGY STORAGE DEVICE” and publishedJul. 9, 2015.

In some embodiments, the storage cell 12 is formed into one of a woundform or prismatic form which is then packaged into a cylindrical orprismatic housing 7. Once the electrolyte 6 has been included, thehousing 7 may be hermetically sealed. In various examples, the packageis hermetically sealed by techniques making use of laser, ultrasonic,and/or welding technologies. In addition to providing robust physicalprotection of the storage cell 12, the housing 7 is configured withexternal contacts to provide electrical communication with respectiveterminals 8 within the housing 7. Each of the terminals 8, in turn,provides electrical access to energy stored in the energy storage media1, generally through electrical leads which are coupled to the energystorage media 1.

As discussed herein, “hermetic” refers to a seal whose quality (i.e.,leak rate) is defined in units of “atm-cc/second,” which means one cubiccentimeter of gas (e.g., He) per second at ambient atmospheric pressureand temperature. This is equivalent to an expression in units of“standard He-cc/sec.” Further, it is recognized that 1 atm-cc/sec isequal to 1.01325 mbar-liter/sec. Generally, the ultracapacitor 10disclosed herein is capable of providing a hermetic seal that has a leakrate no greater than about 5.0×10⁻⁶ atm-cc/sec, and may exhibit a leakrate no higher than about 5.0×10⁻¹⁰ atm-cc/sec. It is also consideredthat performance of a successfully hermetic seal is to be judged by theuser, designer or manufacturer as appropriate, and that “hermetic”ultimately implies a standard that is to be defined by a user, designer,manufacturer or other interested party.

Leak detection may be accomplished, for example, by use of a tracer gas.Using tracer gas such as helium for leak testing is advantageous as itis a dry, fast, accurate and non destructive method. In one example ofthis technique, the ultracapacitor 10 is placed into an environment ofhelium. The ultracapacitor 10 is subjected to pressurized helium. Theultracapacitor 10 is then placed into a vacuum chamber that is connectedto a detector capable of monitoring helium presence (such as an atomicabsorption unit). With knowledge of pressurization time, pressure andinternal volume, the leak rate of the ultracapacitor 10 may bedetermined.

In some embodiments, at least one lead (which may also be referred toherein as a “tab”) is electrically coupled to a respective one of thecurrent collectors 2. A plurality of the leads (accordingly to apolarity of the ultracapacitor 10) may be grouped together and coupledto into a respective terminal 8. In turn, the terminal 8 may be coupledto an electrical access, referred to as a “contact” (e.g., one of thehousing 7 and an external electrode (also referred to herein forconvention as a “feed-through” or “pin”)). Suitable exemplary designsare provided in International Publication No. WO 2015/102716 entitled“ADVANCED ELECTROLYTES FOR HIGH TEMPERATURE ENERGY STORAGE DEVICE” andpublished Jul. 9, 2015.

Various forms of the ultracapacitor 10 may be joined together. Thevarious forms may be joined using known techniques, such as weldingcontacts together, by use of at least one mechanical connector, byplacing contacts in electrical contact with each other and the like. Aplurality of the ultracapacitors 10 may be electrically connected in atleast one of a parallel and a series fashion.

As used herein the symbol “wt %” means weight percent. For example, whenreferring to the weight percent of a solute in a solvent, “wt %/” refersto the percentage of the overall mass of the solute and solvent mixturemade up by the solute.

The entire contents of each of the publications and patent applicationsmentioned above are incorporate herein by reference. In the event thatthe any of the cited documents conflicts with the present disclosure,the present disclosure shall control.

While the invention has been described with reference to exemplaryembodiments, it will be understood that various changes may be made andequivalents may be substituted for elements thereof without departingfrom the scope of the invention. For example, in some embodiments, oneof the foregoing layers may include a plurality of layers there within.In addition, many modifications will be appreciated to adapt aparticular instrument, situation or material to the teachings of theinvention without departing from the essential scope thereof. Therefore,it is intended that the invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thisinvention, but that the invention will include all embodiments fallingwithin the scope of the appended claims.

What is claimed is:
 1. An energy storage apparatus comprising: an activelayer comprising: a network of carbon nanotubes defining void spaces;and a carbonaceous material located in the void spaces and bound by thenetwork of carbon nanotubes; and an adhesion layer disposed between theactive layer and an electrically conductive layer, wherein the adhesionlayer is at least ninety percent single wall carbon nanotubes (SWNT) byweight; wherein the active layer is configured to provide energystorage; wherein the active layer is substantially free from bindingagents and consists essentially of carbonaceous material; wherein theactive layer is bound together and to the adhesion layer byelectrostatic forces between the carbon nanotubes and the carbonaceousmaterial; wherein the network of carbon nanotubes makes up less than tenpercent by weight of the active layer; wherein the network of carbonnanotubes comprises an electrically interconnected network of carbonnanotubes exhibiting connectivity above a percolation threshold. whereinsaid interconnected network of carbon nanotubes comprises one or morehighly conductive pathways, said pathways having a length greater than100 μm; wherein said interconnected network of carbon nanotubes includesone or more structures formed of said carbon nanotubes, said structurehaving an overall length at least ten times the average length ofcomponent carbon nanotubes making up the structure.
 2. The apparatus ofclaim 1, wherein the carbonaceous material comprises activated carbon.3. The apparatus of claim 1, wherein the carbonaceous material comprisesnanoform carbon other than carbon nanotubes.
 4. The apparatus of claim1, wherein the interconnected network of carbon nanotubes comprisesconductive paths configured to facilitate current flow within andthrough the active layer.
 5. The apparatus of claim 4, wherein the longconductive paths have a length on the order of a thickness of the activelayer.
 6. The apparatus of claim 1, wherein the network of carbonnanotubes makes up less than 1% by weight of the active layer.
 7. Theapparatus of claim 1, wherein the network of carbon nanotubes makes upless than 5% by weight of the active layer.
 8. The apparatus of claim 7,wherein the adhesion layer consists essentially of carbon nanotubesdisposed between the active layer and the electrically conductive layer.9. The apparatus of claim 8, wherein a surface of the electricallyconductive layer facing the adhesion layer comprises a roughened ortextured portion.
 10. The apparatus of claim 8, wherein a surface of theelectrically conductive layer facing the adhesion layer comprises ananostructured portion.
 11. The apparatus of claim 10, wherein thenanostructured portion comprises carbide nanowhiskers.
 12. The apparatusof claim 1, wherein the active layer has been annealed to reduceimpurity content.
 13. The apparatus of claim 1, wherein the active layerhas been compressed to deform at least a portion of the network ofcarbon nanotubes and carbonaceous material.
 14. The apparatus of claim1, wherein the highly conductive pathways comprise pathways having alength greater than 500 μm.
 15. The apparatus of claim 1 wherein thehighly conductive pathways comprise pathways having a length greaterthan 500 μm.
 16. The apparatus of claim 1 wherein the highly conductivepathways comprise pathways having a length greater than 1,000 μm. 17.The apparatus of claim 1, wherein the interconnected network of carbonnanotubes includes a structure formed from component carbon nanotubesthat has an overall length at least 100 times the average length of thecomponent carbon nanotubes making up said structure.
 18. The apparatusof claim 17, wherein with the highly conductive pathways have a lengthon the order of the size of the active storage layer.
 19. Anultracapacitor comprising: a pair of electrodes separated by a permeableseparator; and an electrolyte wetting the electrodes and the separator;wherein an active layer of each of the electrodes comprises: a networkof carbon nanotubes defining void spaces; and a carbonaceous materiallocated in the void spaces and bound by the network of carbon nanotubes;and an adhesion layer disposed between the active layer and a currentcollector, wherein the adhesion layer is at least ninety percent singlewall carbon nanotubes (SWNT) by weight; wherein the active layer isconfigured to provide energy storage; wherein the active layer issubstantially free from binding agents and consists essentially ofcarbonaceous material; wherein the active layer is bound together and tothe adhesion layer by electrostatic forces between the carbon nanotubesand the carbonaceous material; wherein the network of carbon nanotubesmakes up less than ten percent by weight of the active layer; whereinthe network of carbon nanotubes comprises an electrically interconnectednetwork of carbon nanotubes exhibiting connectivity above a percolationthreshold. wherein said interconnected network of carbon nanotubescomprises one or more highly conductive pathways, said pathways having alength greater than 100 μm; wherein said interconnected network ofcarbon nanotubes includes one or more structures formed of said carbonnanotubes, said structure having an overall length at least ten timesthe average length of component carbon nanotubes making up thestructure.
 20. The apparatus of claim 19, wherein the ultracapacitor hasan operating voltage of at least 3.0 V.
 21. The apparatus of claim 19,wherein the ultracapacitor has an operating voltage of at least 3.2 V.22. The apparatus of claim 19, wherein the ultracapacitor has anoperating voltage of at least 4.0 V.
 23. The apparatus of claim 19,wherein the ultracapacitor has a maximum operating temperature of atleast 250 C at an operating voltage of at least 2V for a lifetime of atleast 1,000 hours.
 24. The apparatus of claim 19, wherein theultracapacitor has a maximum operating temperature of at least 250 C atan operating voltage of at least 3V for a lifetime of at least 1,000hours.
 25. The apparatus of claim 19, wherein the ultracapacitor has amaximum operating temperature of at least 250 C at an operating voltageof at least 4V for a lifetime of at least 1,000 hours.
 26. The apparatusof claim 19, wherein the ultracapacitor has a maximum operatingtemperature of at least 300 C at an operating voltage of at least 1V fora lifetime of at least 1,000 hours.
 27. The apparatus of claim 19,wherein the ultracapacitor has a maximum operating temperature of atleast 300 C at an operating voltage of at least 2V for a lifetime of atleast 1,000 hours.
 28. The apparatus of claim 19, wherein theultracapacitor has a maximum operating temperature of at least 300 C atan operating voltage of at least 3V for a lifetime of at least 1,000hours.
 29. The apparatus of claim 19, wherein the ultracapacitor has amaximum operating temperature of at least 300 C at an operating voltageof at least 4V for a lifetime of at least 1,000 hours.